Honestly, mine is either Skarmory or Electabuzz. Legendaries are never any trouble. The three birds are a complete joke with how easy they are to get, and Mewtwo is just hard to calculate your chances on. Skarmory because it's ****ing impossible to catch after being impossible to find, and Electabuzz for almost the same reason.
Also, Dratini.
Dratini.
Dratini.